Re: [PATCH] device core: fix dma_mask handling in platform_device_register_full

[Robin Murphy]

On 11/03/2020 4:07 pm, Christoph Hellwig wrote:
> Ever since the generic platform device code started allocating DMA masks
> itself the code to allocate and leak a private DMA mask in
> platform_device_register_full has been superflous.  More so the fact that
> it unconditionally frees the DMA mask allocation in the failure path
> can lead to slab corruption if the function fails later on for a device
> where it didn't allocate the mask.  Just remove the offending code.

I'm sure I mentioned this in passing at the time, but only in the 
context of a cleanup; I never noticed it could be cause for an actual bug :)

Reviewed-by: Robin Murphy <robin.murphy@xxxxxxx>

> Fixes: cdfee5623290 ("driver core: initialize a default DMA mask for platform device")
> Reported-by: Artem S. Tashkinov <aros@xxxxxxx>
> Tested-by: Artem S. Tashkinov <aros@xxxxxxx>
> ---
>   drivers/base/platform.c | 14 --------------
>   1 file changed, 14 deletions(-)
>
> diff --git a/drivers/base/platform.c b/drivers/base/platform.c
> index 7fa654f1288b..47d3e6187a1c 100644
> --- a/drivers/base/platform.c
> +++ b/drivers/base/platform.c
> @@ -662,19 +662,6 @@ struct platform_device *platform_device_register_full(
>   	pdev->dev.of_node_reused = pdevinfo->of_node_reused;
>   
>   	if (pdevinfo->dma_mask) {
> -		/*
> -		 * This memory isn't freed when the device is put,
> -		 * I don't have a nice idea for that though.  Conceptually
> -		 * dma_mask in struct device should not be a pointer.
> -		 * See http://thread.gmane.org/gmane.linux.kernel.pci/9081
> -		 */
> -		pdev->dev.dma_mask =
> -			kmalloc(sizeof(*pdev->dev.dma_mask), GFP_KERNEL);
> -		if (!pdev->dev.dma_mask)
> -			goto err;
> -
> -		kmemleak_ignore(pdev->dev.dma_mask);
> -
>   		*pdev->dev.dma_mask = pdevinfo->dma_mask;
>   		pdev->dev.coherent_dma_mask = pdevinfo->dma_mask;
>   	}
> @@ -700,7 +687,6 @@ struct platform_device *platform_device_register_full(
>   	if (ret) {
>   err:
>   		ACPI_COMPANION_SET(&pdev->dev, NULL);
> -		kfree(pdev->dev.dma_mask);
>   		platform_device_put(pdev);
>   		return ERR_PTR(ret);
>   	}